What is the idea Chaucer wishes to convey in "The Nonnes Preestes Tale"?
Chaucer is very often direct in the pronouncement of his objectives and what he wishes to convey. This directness holds true for "The Nonnes Preestes Tale." First, Chauntecleer expresses Chaucer's message. At the end of the tale, Chauntecleer says that he can only be tricked once because God doesn't take kindly to individuals who willfully get duped by evil doers. In other words, once may be an accident, but twice is intention. Chauntecleer also makes it clear that flattery is a device of evil doers to trick a good individual into ruin.
"I shrewe myself bothe blood and bones,
If thou bigyle me ofter than ones.
Thou shalt namoore, thurgh thy flaterye,
Do me to synge and wynke with myn eye;
665 For he that wynketh whan he sholde see,
Al wilfully, God lat him nevere thee."
The Fox confirms this in a sort of backward way. He says that God is pushed back by and calamity occurs to those who fail to rightly govern their behavior:
God yeve hym meschaunce,
That is so undiscreet of governaunce
In the end, the nun's priest redirects the focus slightly when he expresses Chaucer's objective and message as being that the tale is meant to lead listeners to being good and moral individuals. This redirection of focus does not contradict but gives broader definition to what Chauntecleer and the Fox said.
674 Taketh the moralite, goode men;
Taketh the fruyt, and lat the chaf be stille.
Now goode God, if that it be thy wille,
... make us alle goode men,
680 And brynge us to his heighe blisse ....